The field of art to which this invention pertains is conductive plastics and a process for producing conductive plastic articles.
It is well known in the art that plastics can be made conductive by the incorporation of carbon black. See, for example, U.S. Pat. Nos. 4,465,616, 4,526,952, and 4,559,164. It is well known that thermoplastic compositions can be made electrically conductive by the incorporation of carbon and metallic fibers into a thermoplastic resin matrix.
U.S. Pat. No. 3,687,881 discloses that zinc dust may be added to synthetic and natural rubbers to promote resistance of the rubbers to aging and reversion. It, however, does not disclose that zinc dust may be used to prepare conductive polymer compositions.
U.S. Pat. No. 4,642,202 discloses that metal powders or particles may be used alone or with carbon black to prepare conductive rubber compositions. U.S. Pat. No. 4,552,688 discloses electroconductive silicon elastomer compositions wherein nickel coated carbon is added to a silicon elastomer to prepare a composition having a low resistivity. In U.S. Pat. No. 4,545,926, various polymer compositions are rendered conductive by the dispersion of conductive particles, such as various metal particles, within the polymeric material. U.S. Pat. No. 3,440,181 discloses that electrically conductive polymer compositions may be produced by uniformally dispersing from five to sixty weight percent of metal coated vermicular graphite into a solid organic polymer. However, none of these patents discloses a process whereby plastic articles are made conductive by the incorporation of metal coated plastic pellets into the plastic articles.
In order to apply coatings to plastics, various approaches have been taken in the prior art. For example, in Canadian Pat. No. 744,024, a primer coating composition for acetal plastic surfaces is disclosed. The composition is comprised of a film forming polymer, a phosphoric acid ester, and a boron trifluoride catalyst. The composition is applied to an acetal article and then baked to form a primer coating to which decorative coatings can be applied.
U.S. Pat. No. 3,141,789 discloses a coating composition for coating polyoxymethylene. The composition is comprised of a nitrocellulose, a sulfonamide, a formaldehyde resin former and a non-volatile acid. After the composition is applied to a polyoxymethylene substrate, it is baked to form a coating to which a variety of top coats can be applied.
U.S. Pat. No. 3,595,718 discloses a process for etching plastic surfaces, such as acetal surfaces. A high surface carrier, such as diatomaceous earth, that has been impregnated with an etching agent, such as an organic or inorganic acid, is used to treat a plastic article. The article can be buried in a bed of the impregnated carrier. After treatment, the article is more receptive to coatings.
In U.S. Pat. No. 4,418,162, a method for treating the surface of polyacetal resin articles is disclosed. The article is treated with an acidic solution containing hydrochloric and sulfuric acid. After such treatment, the article can be non-electrically plated with a nickel plating solution. The patent also discloses that the polyacetal resin preferably contains calcium carbonate.
U.S. Pat. No. 3,414,427 discloses a method for catalysing the surface of a material to be plated with metal. The surface is first immersed in a catalyst solution containing a complex of palladium chloride with hydrogen halide and water dissolved in an organic solvent and then is immersed in a plating bath, such as a nickel hypophosphite bath. The patent, however, does not disclose that the article should be etched in an acid bath before being treated with the catalysing solution.
In U.S. Pat. No. 4,066,809, a process for preparing a dielectric material for electroless deposition of a conductive material thereon is disclosed. The process consists of contacting a dielectric substrate with a stannous chloride sensitizing solution to deposit a layer of tin cations on the substrate, rinsing the stannous chloride from the substrate with hot water, contacting the substrate with a palladium chloride activator, contacting the substrate with a palladium chloride/stannous chloride/hydrochloric acid seeder bath, baking and then coating the substrate. The patent, however, does not disclose that the article should be etched with acid before being treated with a palladium-tin catalyst solution.
None of these patents relating to the coating of plastics, however, discloses a process whereby metal particles can be incorporated into a plastic article to render the article conductive.
One of the problems in the prior art with the use of carbon black to make plastic articles conductive is that the handling of carbon black can cause environmental problems, such as air pollution and breathing problems. Another problem is that when metal powder is used to make plastic articles conductive, the density difference between the powder and the plastic polymer can result in a settling of the metal powder so that a non-uniform distribution of metal particles within the article results.
Accordingly, it is an object of this invention to prepare plastic articles wherein there is a uniform distribution of metal particles within the article.
It is a further object of this invention to prepare condutive plastic articles.
These objects are obtained by the process of this invention.